I downloaded a new copy of what they call 1809. The version is totally confusing and I have not idea what t means. ![Huh? ???](https://www.computerhope.com/forum/Smileys/classic/huh.gif)
The "version" that is part of the name is just YYMM for the initial availability. 1809 is the "October Update" from last year. eg. 9th month of 2018
The build number is 18290.1000 and I was told in school that you never put trailing zero on a decimal friction, unless it is currency.
As you should know version numbers aren't decimals. 18290.1000 is a later version than 18290.999. The decimal/period is merely a separator for the different parts of the version which are (effectively) the place values.
Given your use case you should not join the Insider program (Reinstalling may have effectively done so, but you might want to double-check). Unless you know there are specific features you need (And it sounds like you have the opposite issue), or you want to be the guinea pig filling in for Microsoft's laid off QA Staff, it doesn't make sense.
The option to leave is found in Settings, Updates & Security, and on the left "Windows Insider Program" where there is an option to stop receiving insider builds (or start getting them, if you aren't).
The latest "Stable" Windows 10 ISO can be found
here. Currently this is 17763.253.